Piezoelectric body film, piezoelectric body film production method, and piezoelectric body device

Abstract

To provide a piezoelectric body film that can suppress decrease in the piezoelectric constant d 31 , a method of producing a piezoelectric body film, and a piezoelectric body device. A piezoelectric body film comprising a fluororesin as a piezoelectric material, the fluororesin containing, as a main constituent unit, a repeating unit derived from vinylidene fluoride, a piezoelectric constant d 31 of the piezoelectric body film being 20 pC/N or greater, and an extrapolated onset temperature at start of shrinkage determined by TMA measurement being not lower than 90° C. and not higher than 115° C. The difference between piezoelectric constants d 31 measured before and after heating the piezoelectric body film at 100° C. for 24 hours relative to the piezoelectric constant d 31 before the heating for 24 hours is 20% or less.

The invention claimed is: 
     
       1. A method of producing a piezoelectric body film, the method comprising:
 forming a film, the forming including forming a crystalline polymer film having piezoelectricity by subjecting a sheet to stretching treatment and polarization treatment, the sheet being formed from a fluororesin containing a repeating unit derived from vinylidene fluoride as a main constituent unit; 
 performing relaxation including performing heat fixation and relaxation of residual strain of the crystalline polymer film by subjecting the crystalline polymer film to heating at a first temperature that is not lower than 90° C. and not higher than 115° C. for not less than 5 seconds and not more than 130 seconds; and 
 performing a secondary heating including subjecting the crystalline polymer film after the performing relaxation to reheating at a temperature that is not lower than the first temperature and not higher than 140° C. for not less than 15 seconds and not more than 120 seconds, and producing the piezoelectric body film. 
 
     
     
       2. The method of producing a piezoelectric body film according to  claim 1 , wherein, in the performing the secondary heating, heating of the crystalline polymer film is performed at the first temperature. 
     
     
       3. A method of producing a piezoelectric body film from a crystalline polymer sheet,
 the method comprising: 
 forming a film, the forming including forming a crystalline polymer film having piezoelectricity by subjecting a sheet to stretching treatment and polarization treatment, the sheet being formed from a fluororesin containing a repeating unit derived from vinylidene fluoride as a main constituent unit; and 
 performing relaxation including performing heat fixation and relaxation of residual strain of the crystalline polymer film by subjecting the crystalline polymer film to heating at a temperature higher than 115° C. and not higher than 150° C. for not less than 10 seconds and not more than 140 seconds.